Various herbicides, such as, for example, those of the sulfonamide and sulfonylurea classes are known to be active as selective pre- and post-emergent weed control agents. Many times when certain of these compounds are employed at the dosage rates usually necessary for the control of many of the broadleaf and/or grassy weeds, serious loss of many grass crop plants occur.
One procedure to overcome the above indicated sensitivity responses of plants to the various herbicidal compounds involves varying the dosage rate. When a reduction in the dosage rate is used to avoid phytotoxicity to the crop plants, reduced weed control is often the result.
Another procedure involves changing the time of application or modifying the ingredients used in the formulations containing the active compound. Other known procedures include treatment of the seeds of the crop plants with an agent antagonistic to the herbicide prior to planting as described in U.S. Pat. No. 3,131,509.
It has now been found that the pre- and post-emergent phytotoxicity of certain sulfonamide and sulfonylurea herbicides towards grass crop plants is reduced by admixing said herbicides with a herbicidal organic acid in an amount sufficient to reduce the pH of the mixture to below 5. The herbicidal acids are from the group consisting of clopyralid, 2,4-D, 2,4-DP and its optical isomer dichlorprop-P, dicamba, fluroxypyr, MCPA, MCPP and its optical isomer mecoprop-P, picloram, and triclopyr or mixtures of said acids. It has further been discovered that the known salts and esters of these acids do not offer the same protection to the crop plants as afforded by the acid form of said compounds.